Systems are known for feeding preforms to machines such as, for example, blow-molding machines, and in such systems the preforms are allocated at a containment hopper from which they are picked up by elevator trays which, in turn, feed them to a feeder device which usually comprises two alignment rollers which are inclined with respect to the horizontal and are substantially mutually parallel.
The two rollers are made to rotate in mutually opposite directions and are mutually spaced apart so as to leave an interspace between the two rollers which is slightly larger than the transverse size of the body of the preforms.
Such interspace is still smaller than the size of the support flange arranged at the base of the neck of the preform.
Such systems are configured so that, under the effect of gravity, the preforms are made to arrange themselves between the two rollers, so that the body of the preform extends, downwardly, into the interspace defined between the rollers and so that the corresponding flange is resting on the rollers: the rotary motion of the rollers and their inclination tend to bring the preforms, one after the other, into the position described above.
Downstream of the rollers, the preforms are brought to a conveyor guide which is constituted by two conveyance rails, which are designed to feed the preforms to a machine, for example to a blow-molding machine.
Since the preforms are unloaded in a disorderly manner onto the alignment rollers, some of them will arrive at the conveyance rails without being arranged correctly.
This is the reason why known systems for feeding preforms comprise filtration means, for example constituted by brushes, the purpose of which is to eliminate such preforms from the rollers.
In order to improve, in conventional systems for feeding, the elimination of incorrectly positioned preforms, the document WO2002/036466 discloses the possibility of using, in order to eliminate the incorrectly arranged preforms, an expulsion wheel arranged above the rollers so as to discard the incorrectly positioned preforms and, specifically, preforms inserted one inside the other and vertically or preforms lying horizontally and above the correctly arranged preforms.
Such solution is however not fully satisfactory, in that it does not succeed in eliminating all types of incorrectly positioned preforms.
In fact, in some cases the preforms arrange themselves laid flat and oriented longitudinally, i.e. parallel to the axes of the rollers and of the conveyance rails.
In these cases, the preforms are not eliminated with conventional devices and, consequently, they are fed to the blow-molding machine, inevitably causing a shutdown of the machine and the necessity of manually removing the preform.
In order to try to solve such drawbacks, a solution has been devised, disclosed in EP1697238 B1 by Sidel, which comprises, in sequence along the longitudinal advancement direction of the preforms, a sorting and alignment device the upper end of which is fed with randomly arranged preforms and the lower end of which comprises at least two alignment rollers, which are substantially parallel and rotatable about the respective axes.
The two alignment rollers are designed to position the preforms in conveyance tracks, which are inclined with respect to the horizontal, in order to feed them to the blow-molding machine.
The system comprises, upstream of the blow-molding machine, filtration means for removing the incorrectly positioned preforms.
Such filtration means comprise, downstream of the alignment rollers, at least one selective removal device which is designed to remove the preforms laid flat individually, which arrive from the alignment rollers on the conveyance tracks and are oriented longitudinally and extend completely longitudinally on the conveyance tracks.
In this manner, the incorrectly aligned preforms are expelled by the alignment system (and recovered at another time), thus preventing a buildup of them on the alignment rollers and a consequent blockage of the machine.
In the solution disclosed and illustrated in EP1697238 B1, the unloading of the preforms occurs when these extend, in a longitudinal direction, wholly on the rails.
The unloading is ensured by the fact that a portion of the rails can move in order to allow, once the interruption in the advancement of the preforms toward the blow-molding machine has been detected, a widening of the interspace between the rails and the unloading of the incorrectly oriented preform (and of those arranged immediately upstream).
However, the solution proposed above does not appear to be devoid of drawbacks either.
In particular, it is necessary to structure the unloading rails so that a portion can be moved on command, with an evident increase of the construction complexity of the system.
Furthermore, in order to be certain that the incorrectly oriented preforms are unloaded, it is necessary that a considerable portion of rail be moveable and this entails, consequently, the unloading of a considerable number of preforms which are correctly aligned, as well.
The aim of the present disclosure is to eliminate, or at least to drastically reduce, the above mentioned drawbacks.
Within this aim, the disclosure provides a system for feeding preforms which makes it possible to unload the incorrectly oriented preforms in an extremely practical and effective manner.
The disclosure further provides a system for feeding preforms which can be implemented without having to intervene on the rails.
This aim and these and other advantages which will become better apparent hereinafter are achieved by providing a system for feeding preforms according to the appended independent claims.